The temperature response of photosystem II quantum yield is an important driver of leaf photosynthesis: a review and data synthesis

Photosystem II quantum yield (φPSII) measures the efficiency with which photosystem II converts absorbed light to photochemistry, and thus variation in φPSII directly affects leaf CO2 assimilation. Given the sensitivity of photosystem II to temperature stress, increasing our understanding of the φPSII temperature response could improve model estimates of terrestrial carbon cycling in an increasingly warm and erratic climate. We reviewed the literature to establish what is known of the φPSII temperature response and highlighted potential underlying physiological and molecular mechanisms. We then used φPSII temperature response data collated from our review to generate a new and improved temperature response function for φPSII. After examining how a subset of land surface models currently represent φPSII and its temperature response, we incorporated our new temperature response function into the Farquhar, von Caemmerer, and Berry C3 photosynthesis model. The model output showed that RuBP-limited photosynthesis is most affected by the φPSII temperature response as leaf temperatures increase or decrease further from the optimum temperature of φPSII. In addition to providing a new φPSII temperature response function, we also highlight key unanswered questions surrounding the φPSII temperature response that, if addressed, could bolster efforts to predict the effects of temperature on photosynthesis.